Sunday, December 7, 2014

Solid as a rock

In a few localities around the Maltese islands it is possible to find what looks like mounds of reddish-brown soil with stones and pebbles embedded in it. On close inspection one realises that what looks like soil is a solid structure as hard as the surrounding rocks. 

These geological features were formed after the Maltese islands emerged from beneath the surface of the sea were they were formed. One can find such structures among other places at Wied Magħlaq and Pembroke.

The Maltese islands are made up of five layers of sedimentary rock. The oldest layer started to be deposited thirty to thirty five million years ago making the Maltese islands relatively young in geological terms.

The topmost layer, therefore the most recent layer to be formed is known as upper coralline limestone is usually more 150 metres thick. The second layer which is made up of Greensand is absent from many areas and which is nowhere thicker than thirteen metres. This is followed by the blue clay layer underneath which one finds the globigerina limestone which can be as thin as 20 metres in some places and thicker than 100 in others. The oldest layer is the lower coralline limestone which is very similar to the upper coralline limestone and which like it is very thick.

Beneath these five layers are even older layers which cannot be seen without drilling through the lower coralline limestone.

 The emergence of the Maltese islands above the surface of the sea did not mean the end of rock formation.

The rocks which formed after the emergence of the islands from the sea are known as quaternary deposits because they were formed during the quaternary period. This period started just over two and a half million years ago. It s defined by a number of ice ages with warm periods in between. This period is divided into two - the Pleistocene which ended about twelve thousand years ago and the Holocene, the period in which we are living. The Holocene is considered as the most recent interglacial warm period.

During the Quaternary sea levels went up end down depending on the temperature. During Ice Ages evaporated water precipitated as snow and ice and formed thick glaciers leading to lower sea levels. In higher temperatures the glaciers melted and sea levels became higher. The low water level uncovered the sea bottom between Malta, Sicily and the Italian mainland creating a large continuous landmass. T

he weather was also characterised by heavy precipitation and the creation of several valleys which were formed by large amounts of flowing water which carry with them large quantities of sediment and debris including soil, pebbles rocks as well as small and large organisms.

The quaternary deposits were carries down such valleys although it is possible that many of them were formed during the Holocene period. 

This article wsa published in The Times of Malta on 30 October 2014.

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